Interannual variation in Neocalanus biomass in the Oyashio waters of the western North Pacific     

KAZUAKI TADOKORO  SANAE CHIBA  TSUNEO ONO  TAKASHI MIDORIKAWA  TOSHIRO SAINO 《Fisheries Oceanography》2005,14(3):210-222

We examined the interannual variation in Neocalanus copepod biomass in the Oyashio waters in spring and summer from 1972 to 1999. In the mid‐1970s, mesozooplankton biomass in spring was high; however, it decreased significantly in the late 1970s. The timing of the decrease in mesozooplankton biomass corresponded to the 1976/77 climatic regime shift. The biomass of N. flemingeri, which dominated the Neocalanus community, was roughly constant from 1980 to 1999. Although species‐level estimates of Neocalanus biomass were not available for the 1970s, a previous study reported that Neocalanus copepods were the predominant mesozooplankton in the Oyashio waters in spring during the 1970s. Neocalanus copepods dominated the mesozooplankton community throughout the 1970s, and their biomass decreased in the late 1970s. Springtime net community production, an index of new production, also decreased in the late 1970s. We suggest that the reduction in new production negatively affected Neocalanus food availability, resulting decreased copepod biomass. New production may have been limited by a combination of subsurface iron supplies, increased vertical density gradient, and reduced vertical water mixing in winter, which resulted in diminished iron entrainment in winter. In summer, mesozooplankton biomass significantly decreased and increased synchronously with the 1976/77 and 1988/89 climatic regime shifts. The biomass of N. plumchrus, which dominated the Neocalanus community, was low in the 1980s and increased in the early 1990s. The biomass of the second‐most dominant copepod, N. cristatus, also increased in the early 1990s. Neocalanus copepods were reported to be a dominant component of the mesozooplankton community in the 1970s; Neocalanus biomass was high in the mid‐1970s and decreased in the late 1970s. Japanese sardine (Sardinops melanostictus), an important predator of Neocalanus copepods, exhibited interannual variation in standing stock that was inversely related to mesozooplankton biomass. At their peak in 1984, sardines consumed 32–138% of the daily Neocalanus production during summer. Therefore, predation pressure on Neocalanus by Japanese sardine is likely to affect interannual variation in mesozooplankton biomass during the summer.  相似文献   

Environmental 'loopholes' and fish population dynamics: comparative pattern recognition with focus on El Niño effects in the Pacific   总被引：1，自引：2，他引：1  

Andrew Bakun  Kenneth Broad 《Fisheries Oceanography》2003,12(4-5):458-473

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Influence of feeding regime on intraspecific competition, fin damage and growth in 1+ Atlantic salmon parr (Salmo salar L.) held in freshwater production cages     

Chris Noble  Sunil Kadri  David F Mitchell  & Felicity A Huntingford 《Aquaculture Research》2007,38(11):1137-1143

The feeding behaviour, growth and feed conversion ratio (FCR) of cage‐held Atlantic salmon parr (Salmo salar L.) were studied when in 576 m³ (12 m × 12 m × 4 m) commercial freshwater cages under ambient water temperature (8.84±3.53°C) and photoperiod (11.02±2.05 h) for 205 days. The effect of feeding regime on fin damage was also investigated. Six groups (n=31 234±2051 fish group⁻¹, initial stocking density 1.25±0.14 kg m⁻³) were fed to satiation using either (a) an imposed regime involving scheduled, fixed ration feeding every 10 min from dawn till dusk or (b) on demand from dawn till dusk using commercial interactive feedback systems. During feeding, there were no significant differences in aggression although swimming speeds and turning angles were significantly higher in fish under the imposed regime. On‐demand feeding significantly reduced the incidence of dorsal fin damage. There was no clear relationship between fish size, feed regime and the incidence of fin damage until 1 week before the fish were transferred to marine cages, when the smallest fish under each feeding regime had the highest incidence of fin damage. Interestingly, growth did not differ between regimes, but fish under the imposed regime were significantly overfed and achieved higher FCRs.  相似文献   

Connectivity,habitat, and flow regime influence fish assemblage structure: Implications for environmental water management in a perennial river of the wet–dry tropics of northern Australia     

Bradley J. Pusey  Michael Douglas  Julian D. Olden  Sue Jackson  Quentin Allsop  Mark J. Kennard 《水产资源保护:海洋与淡水生态系统》2020,30(7):1397-1411

1. Environmental water management seeks to balance competing demands between the water needed to sustain human populations and their economic activities and that required to sustain functioning freshwater ecosystems and the species they support. It must be predicated on an understanding of the environmental, hydrological, and biological factors that determine the distribution and abundance of aquatic species.
2. The Daly River of the wet–dry tropics of northern Australia consists of a perennially flowing main stem and large tributaries, as well as many small to large naturally intermittent tributaries, and associated off‐channel wetlands. Increased groundwater abstraction to support irrigated agriculture during the dry season threatens to reduce dry‐season flows that maintain perenniality and persistence of freshwater fishes.
3. Fish assemblages were surveyed at 55 locations during the dry season over a 2‐year period with the goal of establishing the key landscape‐scale and local‐scale (i.e. habitat) drivers of fish species distribution.
4. Longitudinal (upstream/downstream) and lateral (river/floodplain) gradients in assemblage structure were observed with the latter dependent on the position in the river landscape. Underlying these gradients, stream flow intermittency influenced assemblage composition, species richness, and body size distributions. Natural constraints to dispersal were identified and their influence on assemblage structure was also dependent on position within the catchment.
5. Eight distinct assemblage types were identified, defined by differences in the abundance of species within five groups differing in functional traits describing body size, spawning requirements, and dispersal capacity. These functional groups largely comprised species widely distributed in northern Australia.
6. The results of the study are discussed with reference to the environmental flow needs of the Daly River and other rivers of northern Australia. The findings may also be applied to environmental flow management in savannah rivers elsewhere.

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Floodplains of a regulated southern alpine river (Brenno,Switzerland): ecological assessment and conservation options     

M. Brunke 《水产资源保护:海洋与淡水生态系统》2002,12(6):583-599

• 1. The fifth‐order southern alpine Brenno River and its floodplains are severely impaired by embankments, water abstractions and the construction of dams for hydropower generation. The river's annual mean discharge is reduced to 27% of the natural flow and the number of small (50–100 m³ s^?1) and medium‐sized (101–150 m³ s^?1) floods is reduced significantly.
• 2. Lateral hydrological connectivity has decreased strongly as a result of the flow regulation, whereas the significance of vertical connectivity has increased. The remnants of the middle and lower floodplains still contain springbrooks, ponds, and intermittently connected channels, which are all sustained by emerging groundwater.
• 3. Aquatic floodplain habitats can be classified partially by faunal composition. The lotic/lentic gradient appears to be a dominant compound factor structuring invertebrate assemblages when considering all aquatic habitats. The exfiltration of groundwater in conjunction with a reduced lateral connectivity enables the occurrence of many stenotopic species.
• 4. A comparison of present floodplains with those shown on historical maps shows that the fluvial landscape has changed markedly. The proportions of functional floodplain units characterized by autogenic succession and trends to late successional stages (i.e. senescence) have increased.
• 5. Floodplains of the Brenno river are still considered to represent important ecological areas and they are protected by law. Whilst the legislative protection of floodplains is the basis for conservation, this does not include the restoration of driving hydrological processes. An annual release of small‐ and medium‐sized floods could generate a diversity of disturbances, thereby promoting rejuvenation and counteracting senescence.
• 6. Alternative conservation options that circumvent ongoing contracts of water use, though generally promising, are limited because of the operation of hydropower schemes. At present the exfiltrations of groundwater mitigate the impacts of flow regulation on the ecological integrity of the floodplains.

Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Saiga antelope calving site selection is increasingly driven by human disturbance   总被引：1，自引：0，他引：1  

N.J. Singh  I.A. Grachev  E.J. Milner-Gulland 《Biological conservation》2010,143(7):1770-1779

Many terrestrial mammalian species aggregate to give birth. Such aggregations are likely to be a response to changing resource and water availability, for predator swamping and avoidance of disturbance. The critically endangered saiga antelope (Saiga tatarica) is one such species. We analysed spatio-temporal locations of saiga calving aggregations in Kazakhstan over the last four decades obtained from aerial and ground surveys, to identify the factors determining the selection of calving sites within the species’ range as well as any changes in these locations over time. Generalized mixed models were employed in a use - availability framework to assess the factors distinguishing calving from random sites and predict suitable areas for calving. Saigas selected sites, with lower than average productivity and low year to year variability in productivity, at an intermediate distance from water sources, and away from human settlements. A significant change in calving locations was observed during the last decade, with calving areas occurring further north and further away from settlements than previously. The results demonstrate that the choice of calving areas is largely driven by environmental factors. However, disturbance also has a significant impact on calving site selection and in recent decades, its influence overrides that of environmental factors. This increase in the influence of disturbance coincides with a precipitous decline in saiga numbers due to poaching, as well as substantial reductions in the intensity of land use for livestock grazing following the breakup of the Soviet Union. Predictive models based on such studies can improve species conservation by guiding the stratification of sampling for effective monitoring and deployment of rangers to protect the females at this critical time.  相似文献   

Is colourful self-sustaining forb vegetation mere fantasy?     

《Urban Forestry & Urban Greening》2016

Biodiversity in urban and suburban environments can be supported through establishment of low maintenance-requiring herbaceous vegetation types. Here, we attempt to provide a perspective on the possibilities and limitations of establishing forb-dominated vegetation to support local biodiversity and contribute to changing public aesthetics concerning green spaces. Plant ecological theories, methods and experiences are the foundation for the design and establishment of such vegetation types. We emphasise the importance of high plant density and recurrent disturbance for the maintenance of forb communities. Well-established ecological theory tells us that totally self-sustaining herbaceous vegetation is not a realistic possibility. Without intervention, herbaceous vegetation will change over time and eventually be colonized by woody species through the process of succession. However, by applying a creative and strategic approach to establishment and subsequent management involving small scale disturbances, rather than solely a uniform maintenance regime, it may be possible to maintain a colourful, aesthetically appealing and species-rich forb dominated community that will support biodiversity and increase public acceptance of alternatives to conventional lawns in urban and suburban environments.  相似文献   

Contrasting intraspecific dietary shifts in two terapontid assemblages from Australia’s wet‐dry tropics     

Aaron M. Davis  Bradley J. Pusey  Richard G. Pearson 《Ecology of Freshwater Fish》2012,21(1):42-56

Abstract – This study assessed the size‐related patterns of dietary resource use in terapontid assemblages from two north Australian wet‐dry tropical river systems exhibiting contrasting long‐term flow regimes. Substantially higher size‐related dietary divergence in the form of additional trophic guilds and lower levels of dietary overlap were evident among terapontids from the comparatively stable Daly River system, particularly during the dry season. Relatively restricted expression of size‐related dietary shifts in conjunction with higher levels of dietary overlap and no significant seasonal effects on dietary overlap were features of assemblage interaction in the highly variable Burdekin River. Results highlight size‐related dietary shifts as a complex aspect of terapontid trophic habits, and one that can exhibit considerable spatial dynamism.  相似文献   

论高校合并应处理好的几个关系   总被引：1，自引：1，他引：0  

范惠莹 《高等农业教育》2000,(1):63-66

本从高等教育管理理论的角度，论述了合并大学应处理好个方面的关系；学校与主管部门之间的关系，学校与学院之间的关系，领导与群众之间的关系，一所大学合并成功与否，固然受诸多因素的制药，但关键在于处理那这儿对关系。  相似文献   

Coarse woody debris in late-successional Picea abies forests in northern Europe: Variability in quantities and models of decay class dynamics     

Tuomas Aakala 《Forest Ecology and Management》2010

Coarse woody debris pools and their decay class dynamics were studied in three areas of unmanaged boreal forest in northern Finland, and in the Murmansk and Arkhangelsk provinces in northwestern Russia. The study areas had varying climatic and edaphic conditions, and disturbance histories. Living and dead trees (diameter at 1.3 m height ≥10 cm) were measured in five late-successional Picea abies-dominated stands in each of the three areas. Wood density and time since death were determined from randomly sampled dead P. abies, and their decay class dynamics were modeled using stage-based matrix models.  相似文献